1. Field of the Invention
The present invention relates to diaphragms for electrolytic cells. More particularly, the present invention relates to diaphragms for electrolytic chlor-alkali cells. Even more particularly, the present invention relates to diaphragms from thermoplastic fibers for use in electrolytic chlor-alkali cells.
2. Description of the Prior Art
Asbestos fibers have long been employed as the conventional material for use as diaphragms in chlor-alkali electrolytic cells. Because of the continuous dissolution of asbestos in the cell liquor, asbestos diaphragms have a limited useful life. Furthermore, as is known to those skilled in the art, asbestos diaphragms evidence swelling, thereby necessitating a choice of the distance between the diaphragm and the cathode to accommodate this swelling phenomenon. Moreover, asbestos has a high electrical resistance, thus reducing cell efficiency. Therefore, the prior art has sought suitable replacements for asbestos as the fibrous material for diaphragms.
In seeking suitable replacements for asbestos in electrolytic cells, the prior art has directed its attention to thermoplastic fibers. Thermoplastic fibers maintain diaphragm continuity in the presence of gaseous turbulence within the cell. Generally, the thermoplastic fibers taught as replacements for asbestos have been fluorinated hydrocarbons, such as polytetrafluoroethylene. See, inter alia, U.S. Pat. Nos. 3,312,614 and 3,702,267. Other thermoplastic compounds taught heretofore include the polyalkylene resins, such as polyethylene and polypropylene. See, inter alia, U.S. Pat. No. 3,775,272.
However, in using such materials, the fibers generally are produced by either a melt-spinning or a melt-blowing process, such as described in U.S. Pat. No. 3,755,527. Although these fibers are eminently useful as replacements for asbestos, it is necessary to either cement the fibers to each other or self-bond the fibers, prior to installation in an electrolytic cell. This is an additional preparatory step which increases the cost of manufacture of such diaphragms.
Other prior art teaches the use of waterleaf rubber diaphragms. However, such materials cannot be used in chlor-alkali cells.
Thus, a major advancement in the art would be provided if thermoplastic fibers, requiring no cementing or bonding, could be employed as diaphragms for electrolytic cells, and especially, in chlor-alkali cells.